Within the modern network space, the Synchronous Optical Network (SONET) protocol (and its European equivalent, the Synchronous Digital Hierarchy (SDH)) protocol is a popular mechanism for data transport. Under the SONET/SDH protocol, connections through the network core, and between end-user communications devices, are constructed using a layered model. Each layer (or level) uses connections established at lower levels to build connections spanning progressively larger portions of the network. Within the network core, Section and Line-level connections are established. Section-level connections (commonly referred to as sections) are set-up between topologically adjacent nodes (which may be, for example, cross-connects, regenerators or Add-Drop-Multiplexors) of the network, and correspond to individual hops of an end-to-end connection. Line-level connections (commonly referred to as lines) are set-up between nodes capable of processing line overhead within data signals (e.g. cross-connects or Add-Drop-Multiplexors). Regenerators are usually capable of terminating only sections, whereas cross-connects and Add-Drop-Multiplexors will normally terminate both sections and lines. Lines typically span one or more sections.
An end-to-end connection between nodes at which a data signal is multiplexed and demultiplexed is a path-level connection (usually referred to as a Path). A path commonly spans multiple lines, and may extend beyond the network core to terminate at suitable end-user communications equipment (such as concentrator access switches or service provider routers).
The SONET/SDH protocol provides conventional methods for validating sections, lines and paths. These include section trace, section parity, and line parity checks which implement integrity and validation within one section or one SONET/SDH line. Telecordia TR-253 describes a Path Trace implementation, which enables an end-to-end validation of a path. Path parity implements a path level integrity check. Tandem connection monitoring implements additional integrity checks within the path level. These path-level integrity checks utilize validation, parity and fault indication data that are inserted into Synchronous Payload Envelopes (SPEs) of signals being transported through the path, typically embedded within the path overhead (POH).
Co-pending and co-assigned U.S. patent application Ser. No. 09/539,707 filed on Mar. 31, 2000, and entitled METHOD AND SYSTEM FOR ESTABLISHING CONTENT-FLEXIBLE CONNECTIONS IN A COMMUNICATIONS NETWORK teaches a technique for establishing an open connection (OP-N), mapped across a communications network. The OP-N connection is “concatenatable”, in that an end user can transport arbitrarily concatenated signal traffic through the OP-N connection. In principle, virtually any combination of concatenated and non-concatenated signals may be used, up to the bandwidth capacity of the OP-N connection. The traffic mixture (i.e., the mix of concatenated and non-concatenated traffic) within the OP-N connection can be selected by the end user to satisfy their requirements, and may be changed by the end user as those requirements change, without requiring re-configuration of the OP-N connection.
The OP-N connection described in the above-referenced co-pending patent application is constructed using a layered model, in a manner analogous to conventional SONET/SDH connections. The layers of an OP-N connection are designed to fit between the SONET/SDH Line and Path layers. In general, an OP-N connection is expected to span multiple lines, and yet be shorter than an end-to-end path. An OP-N connection may carry multiple paths and will be set up and validated prior to the establishment of any paths through it. It is therefore necessary to implement a technique for validating OP-N connections independently of any Path-level connections.
Co-pending and co-assigned U.S. patent application Ser. No. 09/597,974, filed on Jun. 20, 2000 and entitled VALIDATION OF A CONNECTION BETWEEN ARBITRARY END-NODES IN A COMMUNICATIONS NETWORK teaches a technique for validating OP-N connections independently of any Path-level connections. Validation of the OP-N connection is accomplished by inserting performance monitor (PM) information into an unused portion of the transport overhead (TOH) of a SONET/SDH data signal at a transmitting end-node of the OP-N connection. At the receiving end-node of the OP-N connection, the PM information is extracted and examined. At each intermediate node between the transmitting and receiving end-nodes, the PM information is extracted from the data signal, buffered while the data signal is pointer processed, and then reinserted before forwarding the data signal. Multiple levels of OP-N connections can be independently validated in this manner, by providing each level with respective PM information.
A disadvantage of this method is the need for extracting, buffering, and reinserting the PM information at intermediate nodes between the transmitting and receiving end-nodes of the OP-N connection. Such complex processing requires specialized hardware and/or software within each node, which significantly increases costs.
Accordingly, a cost-effective method and apparatus for validating an OP-N connection mapped through a communications network between arbitrary end-points remains highly desirable.